mount: Factor out mount tree build for NEWNS and non-NS cases

We anyway build the tree, in the NS case -- few calls later.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-dump.c

@@ -1703,7 +1703,7 @@ int cr_dump_tasks(pid_t pid)
 	if (collect_file_locks())
 		goto err;
 
-	if (collect_mount_info(pid, true))
+	if (collect_mount_info(pid))
 		goto err;
 
 	if (mntns_collect_root(root_item->pid.real))

cr-restore.c

@@ -1260,14 +1260,7 @@ static int restore_task_with_children(void *_arg)
 
 	/* Restore root task */
 	if (current->parent == NULL) {
-		/*
-		 * For ghost file path resolving on BTRFS we will need
-		 * parsed mount tree, but IIF we're not restoring task
-		 * with mount namespace cloned, in this case we don't parse
-		 * mount tree early because we will be reading mount points
-		 * from image later and generate new mount tree.
-		 */
-		if (collect_mount_info(getpid(), !(ca->clone_flags & CLONE_NEWNS)))
+		if (collect_mount_info(getpid()))
 			exit(1);
 
 		if (prepare_namespace(current, ca->clone_flags))

include/mount.h

@@ -7,7 +7,7 @@ extern int mntns_collect_root(pid_t pid);
 struct proc_mountinfo;
 
 extern int open_mount(unsigned int s_dev);
-extern int collect_mount_info(pid_t pid, bool parse);
+extern int collect_mount_info(pid_t pid);
 extern struct fstype *find_fstype_by_name(char *fst);
 
 struct cr_fdset;

mount.c

@@ -70,7 +70,7 @@ int open_mount(unsigned int s_dev)
 	return -ENOENT;
 }
 
-int collect_mount_info(pid_t pid, bool parse)
+int collect_mount_info(pid_t pid)
 {
 	pr_info("Collecting mountinfo\n");
 
@@ -81,16 +81,15 @@ int collect_mount_info(pid_t pid, bool parse)
 	}
 
 	/*
-	 * WARN: Don't ever parse already parsed mount tree,
-	 * this will corrupt mount lists leading to weird
-	 * errors.
+	 * Build proper tree in any case -- for NEWNS one we'll use
+	 * it for old NS clean, otherwise we'll use the tree for
+	 * path resolution (btrfs stat workaround).
 	 */
-	if (parse) {
-		mntinfo_tree = mnt_build_tree(mntinfo);
-		if (!mntinfo_tree) {
-			pr_err("Building mount tree %d failed\n", getpid());
-			return -1;
-		}
+
+	mntinfo_tree = mnt_build_tree(mntinfo);
+	if (!mntinfo_tree) {
+		pr_err("Building mount tree %d failed\n", getpid());
+		return -1;
 	}
 
 	return 0;
@@ -1117,8 +1116,6 @@ static int do_umount_one(struct mount_info *mi)
 
 static int clean_mnt_ns(void)
 {
-	struct mount_info *pm;
-
 	pr_info("Cleaning mount namespace\n");
 
 	/*
@@ -1130,11 +1127,7 @@ static int clean_mnt_ns(void)
 		return -1;
 	}
 
-	pm = mnt_build_tree(mntinfo);
-	if (!pm)
-		return -1;
-
-	return mnt_tree_for_each_reverse(pm, do_umount_one);
+	return mnt_tree_for_each_reverse(mntinfo_tree, do_umount_one);
 }
 
 static int cr_pivot_root()